1. Field of the Invention
This invention relates to improved filter fibers and filters comprising said fibers. More particularly, this invention relates to such filter fibers comprising a polyester and a polyolefin, and filters comprising said fibers.
2. Prior Art
Polyesters are well known materials for the manufacture of fibers. Illustrative of such fibers are those described in U.S. Pat. Nos. 4,454,196; 4,410,473; and 4,359,557.
Polyolefinic materials are well known articles of commerce which have experienced wide acceptance in forming shaped objects and film or sheet material. The use of such materials has extended to the fiber and fabric industries. For example, U.S. Pat. Nos. 4,587,154; 4,567,092; 4,562,869; and 4,559,862.
Fibers containing mixtures of polyolefins and polyesters are known. For example, U.S. Pat. No. 3,639,505 describes fibers and films composed of a polymer alloy comprising an intimate blend of polyolefin, a minor amount of polyethylene terephthalate and 0.2 to 5 parts per hundred parts of polymer of a toluene sulfonamide compound which are described as having improved receptivity to dispersed dyes.
Bicomponent fibers are known in the art. For example, Textile World, Jun. 1986 at page 29 describes sheath/core fibers which have an inner core of polyester and have an outer core of polypropylene or polyethylene. Also see Textile World, Apr. 1986, page 31.
Bicomponent textile filaments of polyester and nylon are known in the art, and are described in U.S. Pat. No. 3,489,641. According to the aforesaid patent, a yarn that crimps but does not split on heating is obtained by using a particular polyester.
It is also known to employ as the polyester component of the bicomponent filament a polyester which is free from antimony, it having been determined that antimony in the polyester reacts with nylon to form a deposit in the spinneret which produces a shorter junction line, and thus a weaker junction line. Such products are claimed in U.S. patent application Ser. No. 168,152, filed Jul. 14, 1980.
It is also known to make bicomponent filaments using poly[ethylene terephthalate/5-(sodium sulfo) isophthalate] copolyester as the polyester component. U.S. Pat. No. 4,118,534 teaches such bicomponents.
It is also known to make bicomponent filaments in which the one component partially encapsulates the other component. U.S. Pat. No. 3,607,611 teaches such a bicomponent filament.
It is also known to produce bicomponent filaments in which the interfacial junction between the two polymeric components is at least in part jagged. U.S. Pat. No. 3,781,399 teaches such a bicomponent filament. Bicomponent filaments having a cross sectional dumbell shape are known in the art. U.S. Pat. No. 3,092,892 teaches such bicomponent filaments. Other nylon/polyester bicomponent fibers having a dumbell cross sectional shape having a jagged interfacial surface, the polyester being an antimony-free copolyester having 5-(sodium sulfo) isophthalate units are known. U.S. Pat. No. 4,439,487 teaches such fibers. The surface of such bicomponent filament is at least 75% of one of the polymeric components. Still other nylon/polyester bicomponent sheath/core fibers are described in Japan Pat. Nos. 49020424, 48048721, 70036337 and 68022350; and U.S. Pat. Nos. 4,610,925, 4,457,974 and 4,610,928.
Fibers have previously been prepared from blends of polyamides with minor amounts of polyesters such as poly(ethylene terephthalate). Intimate mixing before and during the spinning process has been recognized as necessary to achieve good properties in such blended fibers. It is furthermore known that the fine dispersions in fibers of polymer blends are achieved when both phases have common characteristics such as melt viscosity. See D. R. Paul, "Fibers From Polymer Blends" in Polymer Blends, vol. 2, pp. 167-217 at 184 (D. R. Paul & S. Newman, ehs., Academic Press 1978).
Graft and block copolymers of nylon 6/nylon 66, nylon 6/poly(ethylene terephthalates) and nylon 6/poly(butylene terephthalate) have been formed into grafts which can be spun into fibers. For example, U.S. Pat. No. 4,417,031, and S. Aharoni, Polymer Bulletin, vol. 10, pp. 210-214 (1983) disclose a process for preparing block and/or graft copolymers by forming an intimate mixture of two or more polymers at least one of which includes one or more amino functions, as for example a nylon, and at least one of the remaining polymers includes one or more carboxylic acid functions, as for example a polyester, and a phosphite compound; and thereafter heating the intimate mixture to form the desired block and/or graft copolymers. U.S. Pat. No. 4,417,031 disclose that such copolymers can be spun into fibers.
The use of polyester fibers as the filter element for air filters of air breathing engines is known. For example, the use of such fibers is described in Lamb, George, E. R. et al., "Influence of Fiber Properties on the Performance of Nonwoven Air Fillers," Proc. Air Pollut. Control Assoc., vol. 5, pp. 75-57 (Jun. 15-20; 1975) and Lamb, George E. R. et al. "Influence of Fiber Geometry on the Performance of Non Woven Air Filters," "Textile Research Journal," vol. 45 No. 6 pp. 452-463 (1975).